INSECT DEVOURING PLANTS. 223 
digestive fluid, a curious change takes place in the cells of the 
glands, the colouring matter which floats in a fluid, aggregates into 
a solid mass, which changes its shape in the same way as does the 
Ameeba. It had for a long time been observed that the edges of 
the leaves of the plant called Butterwort were sometimes turned 
inwards, and that their sticky surfaces were covered with flies. Mr. 
Darwin Counted as many as 142 insects on 32 leaves. The upper 
surfaces of the leaves are studded with glands supported on foot- 
stalks, and also smaller ones on much shorter stems. These glands 
secrete a glutinous fluid, so viscid that it may be drawn out into 
threads like a spiders web. ‘The incurving of the leaf when 
digesting insects, no doubt serves to form a hollow, in which the 
fluid necessary for the purpose can be retained. ‘The process of 
aggregation, as it is called, here also takes place in the glands when 
an insect is caught, in the same way as in the tentacles of Drosera. 
Speaking of the Bladderwort he said: ‘‘ It was formerly supposed 
that the bladders, which often contain air bubbles, served the 
purpose of floating the plant at the surface of the water ; this, 
however, is not the case, for even if all the air is pressed out of the 
bladders the plant still floats. As I see that the central cells of 
the whole of the plant, stem and leaves, are filled with air, this will 
account for its not sinking. The bladders themselves are about 
the 1-1oth to 1-20th of an inch in diameter, and are somewhat 
oval and compressed, while at the upper part, a little to one side, 
is a mouth of a most beautiful construction. ‘The opening of this 
mouth is horse-shoe shaped, and is surrounded by long branches, 
most delicate hairs, or tentacles. ‘These hairs are perfectly trans- 
parent, and in their cells a distinct molecular motion can be seen 
under a high power of the microscope. ‘There can be no doubt 
but that the office of these tentacles is to attract and entice 
minute creatures, for they are spread out like a net around the 
orifice. The valve itself is a most beautiful piece of mechanism ; 
it consists of a transparent slightly convexed membrane, attached 
by its upper end to the walls of the bladder, but having its lower 
end free. It opens inwards, thus allowing anything to pass in, but 
entirely preventing its returning. On the upper and attached end 
of the valve are situated numerous glandular hairs, not unlike 
those on the leaf of Drosera, but much more delicate. ‘They are 
also continued round the mouth of the bladder, and Mr. Darwin 
thinks their office is to absorb any nourishing fluids which may 
escape from the bladder. Other observers think that they secrete 
something which has the power of attracting insects, and certain it 
is that they are often seen feeding upon them, and returning again 
and again asif fascinated. In the knobs of these hairs protoplasm 
may be seen in constant motion under a high power. ‘Towards 
the free border of the valve are situated four stiff but very delicate 
